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Check Engine Light (will Not Go Off)


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I had two codes for egr and rear o2 sensor. So I cleaned the egr and replaced the rear o2 sensor but the light will not go off. I’ve reset the computer and the light automatically comes back on within a second of starting the car. I brought it get the codes scanned and the two cods keep coming back up. My mechanic sais this is odd because the rear o2 sensor doesn’t start sending signal until the car has cycled and the egr does the same. They don’t turn on when the car is first started. He thought it might be the computer since they light goes on a stays on but i tried another computer and have the same problem.

Any ideas on what this could be? I test the o2 sensor harness coming from the car and its sending a 14V signal and two other voltages much lower readings.

I know the egr modulator is clogged and isnt sending out any vacuum but this wouldn’t be an immediate light would it. Im going to remove the vapor canister tomorrow and see how that looks. Could I blow compressed air through the egr vapor lines to make sure they aren’t clogged? I don’t want to damage any other components. Im at a loss here I really don’t know why these two codes keep coming back. I was hoping it wasn’t a short in the harness. I think this might be the case so ill have my DVOM ready tomorrow.

One other thing if i connect just one of the big plugs in the ecu and try and start the car it wont but there is no check engine light. I don’t know id this means anything? Does anyone happen to have any ecu wiring diagrams or any other diagrams which could help me solve the problem?

Thanks

John

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So this is me talking off the top of my head.

If the O2's set a code when the engine is first started it means they have failed the operational check the computer goes through. Otherwise they would only set the code when the management system enters closed loop operation, which takes a few minutes, as the engine has to achieve a certain temperature. What your mechanic means by "cycled" I don't know.

Chances are it is a wiring fault.

As to EGR function, the EGR valve has a position sensor, and the effect of EGR is checked by the O2 sensors. In other words, if an EGR command by the computer is not seen by the position sensor, then a code is set. If the EGR command is seen, but the O2 sensor does not see the correct exhaust gas composition, then another code is set. So if the EGR valve is moving, but not flowing exhaust gas, then the code will be from the O2.

That's my take on it. Who knows, maybe I am wrong.

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Well i just brought it to school today to check it out and here's what we found out..

On the EGR system the EGR Temp sensor is shot. The resistance is totally off so i guess ill be needing that. The only thing is its dealer only and they want $202 :wacko: for this small temp sensor. I really dont know why its so much it’s a small sensor with 6" of wire coming off it with a plug.

And with the rear o2 sensor there is either a problem with the heating element or wiring (including computer but my teacher doubts it’s the computer). The thing is I bought a new Bosch OEM universal but it still doesn’t work. Should I try and exchange it for a Denso O2 sensor since its more original and Denso makes all the parts on this car. Any thoughts regarding the O2 sensor? Anyone use the Bosch or should I try and get the Denso? I hope NAPA could get me the Denso sensor.

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